Thin insulative material with layered gas-filled cellular structure

ABSTRACT

A lightweight, gas-filled, highly insulative material is incorporated into an article of outdoor gear or apparel (e.g., a camping pad). The insulative material has a layered cellular structure that can be filled with an insulative gas (e.g., air or argon). The insulative material includes two or more layers of cells, which improves insulation (compared to a single layer) by reducing convection for a given thickness. Increasing the thickness without substantially increasing convection results in a better insulator and an improvement in the ability to retain heat.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of U.S. patent applicationSer. No. 12/425,379, filed Apr. 16, 2009 and claims the benefit of U.S.Provisional Patent Applications No. 61/103,246, filed Oct. 7, 2008 andU.S. Provisional Patent Application No. 61,146,301, filed Jan. 21, 2009,all of which are hereby incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention is in the field of thermal insulation materials.More particularly, the present invention relates to layered gas filledthermal insulation. 2. The Relevant Technology

Thermal insulators have long been important for human survival andcomfort in cold climates. The primary function of any thermal insulatoris to reduce heat loss (i.e., heat transfer) from a heat source to acold sink. There are three forms of heat transfer: convection,conduction, and radiation.

Heat loss through convective mixing of gases is caused by the tendencyof a gas to form a rotational mixing pattern between a warmed (i.e.,less dense) region and a cooler (i.e., more dense) region. In aconvection cycle, warmed gas is constantly being exchanged for coolergas. One of the primary ways in which thermal insulators work is throughsuppressing convection by trapping or confining a volume of a gas withinthe insulative material. For example, one of the reasons that afiber-filled parka feels warm is that the air near the wearer's skin iswarmed by body heat and the fibers act to prevent or at least slowconvective mixing of the warmed layer of the air with the cold airoutside.

Conduction involves heat flow through a material from hot to cold in theform of direct interaction of atoms and molecules. For example, thephenomenon of conduction is one of the reasons why a thin layer ofinsulation does not insulate as well as a thicker layer.

Radiation involves direct net energy transfer between surfaces atdifferent temperatures in the form of infrared radiation. Radiation issuppressed by using materials that reflect infrared radiation. Forexample, the glass surface of a vacuum flask is coated with silver toreflect radiation and prevent heat loss through the vacuum region.

Different thermal insulators prevent heat loss through convection,conduction, and radiation in different ways. For example, fiber-basedthermal insulators like polyester fiber fill or fiberglass insulationutilize fairly low conductivity fibers in a stack or batt with a volumeof air trapped or confined amongst the fibers. Furthermore, conductionis reduced by the random orientation of the fibers across the stack orbatt, and radiative heat loss is somewhat reduced because the radiationis scattered as it passes through the fibers.

Another example class of thermal insulators includes closed cellstructures, such as foams or microspheres. Closed cell structures aregenerally comprised of a polymer matrix with many small, mostly closedcavities. As with fiber-based insulations, these insulators conserveheat by trapping a volume of air in and amongst the cells. In fact,convection is effectively eliminated inside the small, closed cells.Furthermore, conduction is reduced by using low conductivity materials,and radiation is low because the cells are typically very small andthere is little temperature difference between cavity walls and hencelow driving force for radiative heat transfer.

Essentially all thermal insulators present a tradeoff between insulativevalue (i.e., prevention of convection, conduction, and radiation), bulk,and cost. For example, because of the bulkiness of fiber- or foam-basedinsulation, achieving a sufficient degree of insulation for a given setof conditions can be difficult without also making the article too bulkyfor practical use. It should also be appreciated that adding additionalfiber- or foam-based insulation inevitably adds weight. Such insulativematerials are also static in that the amount of insulative materialcannot be changed or adjusted as the user's needs change. For example,if a person is wearing a fiber filled parka or sleeping in a fiberfilled sleeping bag, the amount of insulation cannot be increased ordecreased as environmental or activity conditions change.

In addition, many typical insulative materials produce toxic and/orenvironmentally damaging byproducts in the process of manufacture. Forexample, the manufacturing process for many thermal insulators such aspolyester fibers or foams produces CFCs and/or greenhouse gases. Manytypical thermal insulators also continue to outgas toxic chemicals longafter their manufacture. For example, fiberglass insulation is typicallymanufactured with formaldehyde compounds that continue to outgas longafter the insulation is placed in a wall or other structure. And manytypical insulators, such as fiberglass or polyester fiber fill, produceloose fibers that can be harmful if they are inhaled.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a lightweight, gas-filled, highlyinsulative material incorporated into an article of outdoor gear orapparel (e.g., a sleeping pad for camping). The insulative material hasa layered cellular structure that can be filled with an insulative gas(e.g., air or argon). The two or more layers of cells improve insulation(compared to a single layer) by reducing convection for a giventhickness. Increasing the thickness without substantially increasingconvection results in a better insulator and an improvement in theability to retain heat.

In one embodiment, insulation with two or more layers also allows theseams created from the individual cells in one layer to be insulated.Insulated seams may be achieved by offsetting or overlapping the cellsof one layer with the seams of the underlying layer. Insulating theseams of the cellular structure can have a substantial impact onincreasing the insulative value of the material.

In one embodiment, the present invention is directed to a layeredinsulative material that includes first and second gas impermeablelayers joined together to form a chamber having a cell structure andincluding a plurality cells that are in fluid communication. One or moreinterior layers of material are positioned within the chamber betweenthe first and second gas impermeable layers. The one or more interiorlayers divide the chamber into the plurality of cells. The plurality ofcells form a first layer of cells above a second layer of cells. Theinsulative material also includes a valve mechanism coupled to theinsulative material that allows the insulative material to be inflatedor deflated.

In one embodiment, the first and second gas impermeable layers mayinclude a woven material. To make the woven material gas impermeable alaminate may be applied to the surface thereof. In one embodiment, thegas impermeable laminate material may be selected from the groupincluding polyethylene, polypropylene, polyurethane, urethane, siliconerubber, latex rubber, polytetrafluoroethylene (PTFE), expanded PTFE,butyl rubber, and/or Mylar.

In one embodiment, the insulative cell structure of the presentinvention may be used to insulate outdoor apparel. Example outdoorapparel items include, but are not limited to, coats, parkas, jackets,vests, gloves, mittens, hats, liners, waders, snow boots, work boots,ski boots, and snowboard boots.

In another embodiment, the cell structure of the present invention maybe used to insulate outdoor gear. Exemplary outdoor gear items include,but are not limited to, tents, sleeping bags, bivouac bags, and sleepingpads.

The novel insulative materials of the invention may be particularlyadvantageous for use with sleeping pads. Thus, in one embodiment, asleeping pad incorporating a layered insulative material is provided.The sleeping pad includes a sleeping surface sized and configured tosupport a person. The sleeping pad includes a layered insulativematerial including first and second gas impermeable layers joinedtogether to form a chamber having a cell structure comprising aplurality cells that are in fluid communication. The sleeping pad alsoincludes one or more interior layers of material positioned within thechamber between the first and second gas impermeable layers, the one ormore interior layers dividing the chamber into the plurality of cells,wherein the plurality of cells form a first layer of cells above asecond layer of cells. The sleeping pad also includes a valve mechanismcoupled to the insulative material and configured to allow inflation anddeflation of the plurality of cells of the first and second layers ofcells.

In one embodiment, the sleeping pad can include woven materials that arelaminated to provide gas impermeability. The layered cells of thesleeping pad may also be offset or overlapping such that seams in thedifferent layers of cells overlap with one another to reduce heattransfer.

These and other objects and features of the present invention willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of the invention as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic of single insulating gas cell having X,Y, and Z dimensions, a gas reservoir, and a valve;

FIG. 2 illustrates an arrangement of a plurality of insulating gas cellsas in FIG. 1 that are in fluid connection with one another and with agas reservoir;

FIG. 3 illustrates an alternate arrangement of a plurality of insulatinggas cells that are in fluid connection with one another;

FIG. 4 illustrates yet another alternate arrangement of a plurality ofinsulating gas cells that are in fluid connection with one another;

FIG. 5 illustrates even yet another alternate arrangement of a pluralityof insulating gas cells that are in fluid connection with one another;

FIG. 6 illustrates a side cross-sectional view of a plurality ofinsulating cells divided by an intermediate layer;

FIG. 7 illustrates an offset arrangement of a plurality of insulatingcells;

FIG. 8 illustrates a side cross-sectional views of a layered insulatingmaterial with an offset arrangement;

FIG. 9 illustrates a side cross-sectional view of a layered insulatingmaterial with the layers offset arrangement;

FIG. 10 illustrates a spheroidal cell arrangement of a layeredinsulating material;

FIG. 11 illustrates a sleeping pad incorporating a layered insulatingmaterial;

FIG. 12 illustrates a wearable item incorporating the layered insulatingmaterial of FIG. 8;

FIG. 13 illustrates a front cross-sectional view of an air bladderhaving an open cell foam core; and

FIG. 14 illustrates an inflation system for inflating a layeredinsulating material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present disclosure is directed to a lightweight, gas-filled, highlyinsulative material incorporated into an article of outdoor gear orapparel (e.g., a camping pad). The insulative material has a layeredcellular structure that can be filled with an insulative gas (e.g., airor argon). The insulative material includes two or more layers of cells,which improves insulation (compared to a single layer) by reducingconvection for a given thickness. Increasing the thickness withoutsubstantially increasing convection results in a better insulator and animprovement in the ability to retain heat.

I. Design of an Insulative Gas Cell

FIG. 1 illustrates a schematic of single insulating gas cell 10 havingX, Y, and Z dimensions. In a lightweight, gas-filled, highly insulativearticle that depends on the insulating properties of dry gases, theselection of X, Y, and Z dimensions are selected to reduce heat transferby means of convection.

Convective heat transfer consists of both forced and natural convection.Forced convection is due to the induced movement of the gas in thegas-filled cell. For example, in the case of a gas-filled cell that isincorporated into a garment, forced convection can be caused by movementof the wearer. Natural convection is a rotational flow pattern of gascaused by the temperature differential between warm and cool regions ofthe cell and gas buoyancy.

For example, in a gas filled insulating cell 10 like the one depicted inFIG. 1, the gas adjacent to the cell 10 surface nearest to a source ofheat is typically at a higher temperature and lower density than the gasat the surface of the cell closest to atmospheric conditions. The hottergas will rise and the cooler gas will replace the hotter gas thussetting off convective mixing of the gas within the cell 10. This willincrease the heat transfer through the cell 10, which is undesirable forinsulation. For both natural and forced convection, heat transfer isenhanced as the length of the free flowing path of the gas is increased.This is because convective mixing of the gas is allowed to more fullydevelop in these free flowing paths and thus heat transfer by convectionis increased. This means that increasing the XYZ dimensions of the cell10 depicted in FIG. 1 will tend to increase the tendency of convectioncoils to form inside the cell 10, which increases heat loss.

In one embodiment of the present invention, the cell 10 structure isspecifically designed to reduce both free and forced convection of thegas inside the cell 10. Free and forced convection are minimized bychoosing cell volume and dimensions that break up the free flow path ofthe gas inside the cell 10 and thus reduce convective mixing orrotational motion of the gas in the cell 10. In one embodiment of thepresent invention, a heat transfer model was developed that allows oneto predict preferred cell dimensions (i.e., X, Y, and Z dimensions) inorder to minimize natural convection and increase the insulatingcapabilities of the cell 10. These preferred cell dimensions for naturalconvection will also reduce heat transfer due to forced convection.

The model is developed by using both the Rayleigh value and the Nusseltnumber to predict the convective coefficient for the cell 10 understatic conditions (i.e., natural convection and no forced convection).The Rayleigh value is a correlation between the buoyancy and viscousforces of the gas inside the cell 10. Large Rayleigh values areindicative of very buoyant flows leading to increased convection in thecell. Large Rayleigh values would be typical of convective mixing orrotational motion of the gas in large free flowing paths. The Rayleighvalue can be expressed as the following for the geometry used for thecell structure.

$\begin{matrix}{{Ra}_{L} = {\frac{{{gB}\left( {T_{B} - T_{0}} \right)}\delta^{3}}{v^{2}}\Pr}} & (1)\end{matrix}$

In equation 1, g represents gravity, B is the expansion coefficient forthe gas, δ is the thickness of the cell structure when inflated with thegas, P_(r) is the Prandtl number, ν is the kinematic viscosity of thegas, T_(B)−T₀ is the temperature difference between the inner and outerwall of the cell 10. For purposes of this invention, the Rayleigh valueis calculated using a value of 37° C. for T_(B) and −40° C. for T₀.

The Rayleigh value is used in turn to predict the Nusselt number, whichquantifies convective heat transfer from the surfaces of the cell 10.The Nusselt number is then used to calculate the total heat transferthrough the cell 10. Empirical correlations for the average Nusseltnumber for natural convection in enclosures were used to determine theNusselt number based on the Rayleigh value and cell geometry. TheRayleigh value is significantly influenced by the thickness (i.e., the Zdimension depicted in FIG. 1) of the cell 10 and also the temperaturedifference between the inner and outer wall of the cell 10. Increasingthe thickness will increases the free flowing path of the gas. Wheneither the cell thickness or the temperature difference is increasedthan the Rayleigh value is increased which also causes the Nusseltnumber to increase. Equation 2 shows that as the Nusselt number isincreased the total heat transfer in the cell is also increased.

$\begin{matrix}{Q = {{kNuA}\frac{\left( {T_{B} - T_{0}} \right)}{\delta}}} & (2)\end{matrix}$

Equation 2 also shows that the heat transfer through the cell 10 is alsodependent on the facial area of the cell 10 (i.e., A=X·Y). As the facialarea is increased, the heat transfer through the cell 10 is alsoincreased. The equation for heat transfer also shows the importance ofthe thermal conductivity value, k of the gas used in the cell structure.The smaller the thermal conductivity of the gas the lower the total heattransfer through the cell structure. Thermal conductivity of the gas isa function of the gas type (i.e., some gases are better insulators thanother gases), the moisture content of the gas (i.e., increased watercontent increases the thermal conductivity of the gas), and on thetemperature.

One will appreciate from the above discussion that there is an interplaybetween heat loss through convection, as primarily influenced by cellthickness, and heat loss through conduction, as primarily influenced bythe facial area of the cell, along with the thickness of the cell. Inone embodiment, this interplay is balanced leading to a preferred rangefor dimensions of the cell 10. That is, as the cell 10 thickness isincreased heat transfer through conduction is decreased. Nevertheless,there is a point of diminishing returns due to the fact that convectivemixing or rotational motion increases as the cell 10 thickness isincreased. Increased convective mixing and loss of insulation value isseen as an increase in the Rayleigh value for the cell 10. That is, asthe thickness of the cell 10 is increased, there is a point where theincrease in heat transfer due to convection is greater than the decreasein heat transfer due to conduction. After this point there is no longera need to increase the thickness because no benefit in reducing heattransfer can be obtained.

Through use of this theoretical model, it was determined the preferreddimensions for minimal heat transfer through the cell 10 occur at apreferred Rayleigh value less than 300,000. More preferably, theRayleigh value of the cell is in a range from about 50,000 to about275,000. Most preferably, the Rayleigh value of the cell is in a rangefrom about 125,000 to about 250,000. Rayleigh values greater than300,000 will cause the insulative cell to perform less optimally due toconvective heat transfer. This will reduce the effectiveness of the gascell 10 as an insulator.

In one embodiment, the present invention includes a gas-filled, highlyinsulative cell 10. The cell 10 includes a first sheet of a gasimpermeable material and a second sheet of a gas impermeable materialjoined together to form a cell 10. In one embodiment of the presentinvention, the cell 10 depicted in FIG. 1 is attached to a dry gasreservoir 12 and a valve mechanism 16 configured to allow the dryinsulating gas to the introduced into and removed from the cell 10.Additionally, the cell 10, the gas reservoir 12, and the valve mechanismare connected to the cell 10 by means of a gas line 14. As was explainedmore fully in the preceding paragraphs, the volume and XYZ dimensions ofthe cell are chosen such that free and forced convective mixing of gasinside the cell is minimized.

In one embodiment, the cell 10 includes a dry insulative gas disposedwithin the cell 10. The identity of the insulating gas is an importantfactor is determining the insulative properties of the cell 10. Ingeneral, dry gases insulate better than moist gases, monatomic gasesinsulate better than diatomic or polyatomic gases, and heavy, viscousgases insulate better than lighter, less viscous gases. Preferably, thegas disposed within the cell 10 has a moisture content less than about 4percent by weight. More preferably, the gas disposed within the cell 10has a moisture content less than about 2 percent by weight. Mostpreferably, the gas disposed within the cell 10 has a moisture contentless than about 1 percent by weight. The insulating gas can be selectedfrom the group consisting of atmospheric air, argon, krypton, xenon,carbon dioxide, sulfur hexafluoride, and combinations thereof.

In one embodiment, the preferred Rayleigh value for the cell 10 is lessthan 300,000. More preferably, the Rayleigh value of the cell is in arange from about 50,000 to about 275,000. Most preferably, the Rayleighvalue of the cell is in a range from about 125,000 to about 250,000.Based on a preferred Rayleigh value of less than 300,000, preferred X,Y, and Z dimensions for the cell 10 depicted in FIG. 1 were determined.Preferably, the cell volume is less than about 300 cm³ with XYZdimensions of less than about 7 cm by about 14 cm by about 3 cm. Morepreferably, the cell volume is less than about 145 cm³ with XYZdimensions of less than about 4 cm by about 12 cm by about 3 cm. Mostpreferably, the cell volume is less than about 100 cm³ with XYZdimensions of less than about 4 cm by about 8 cm by about 3 cm. Thesedimensions minimize heat transfer due to both forced and naturalconvection.

II. Insulative Material Having Cellular Structure

In one embodiment of the present invention, a plurality of insulativecells as depicted in FIG. 1 are grouped together to form an insulativecell structure. FIGS. 2-10 depict various arrangements of the pluralityof cells 10 that form a cell structure.

With reference to FIG. 2, the cell structure 20 comprises a first sheetof a gas impermeable material and a second sheet of a gas impermeablematerial that are joined together to form a chamber there between. Thechamber is subdivided into a cellular structure comprising a pluralitycells 10. The first and second sheets are bonded together such thatthere are open sections that form the cells 10. In between the cells,there are regions 29 where the first and second sheets are bondedtogether leaving essentially no open space between the first and secondsheets.

In one embodiment, the cells 10 are in fluid communication with oneanother. In the cellular structure depicted in FIG. 2, the cells 10 arein fluid connection with one another via short connector tubes 26 and 28that allow gas to flow between cells 10. It should be mentioned,however, that the connector tubes 26 and 28 do not enhance convectionwithin the cells 10. That is, the connector tubes 26 and 28 aresufficiently small and they are placed such that convection currents donot form between adjacent cells 10.

In one embodiment, a dry insulating gas is disposed within the pluralityof cells 10. The identity of the insulating gas is an important factoris determining the insulative properties of the insulative article 20.In general, dry gases insulate better than moist gases, monatomic gasesinsulate better than diatomic or polyatomic gases, and heavy, viscousgases insulate better than lighter, less viscous gases. Preferably, thegas disposed within the cells 10 has a moisture content less than about4 percent by weight. More preferably, the gas disposed within the cells10 has a moisture content less than about 2 percent by weight. Mostpreferably, the gas disposed within the cells 10 has a moisture contentless than about 1 percent by weight. The insulating gas is selected fromthe group consisting of atmospheric air, argon, krypton, xenon, carbondioxide, sulfur hexafluoride, and combinations thereof.

The insulative article 20 depicted in FIG. 2 is depicted as it may beattached to a dry gas reservoir 12 and a valve mechanism 16 configuredto allow the dry insulating gas to be introduced into and removed fromthe cells 10 comprising the insulative article 20. The insulativearticle 20 is connected to the gas reservoir 12, and the valve mechanism16 via a gas line 14. The connector tubes 26 and 28 depicted in FIG. 2allow gas introduced into one cell 10 to fill all cells 10 in theinsulative article 20.

As was explained more fully in the preceding section, the volume and Xdimension 22, Y dimension 24, and Z dimension (not shown) of the cells10 are chosen such that free and forced convective mixing of gas insidethe cell is minimized. Minimizing free and forced convection of the gasinside the plurality of cells 10 increases the insulative efficiency ofthe insulative article 20. In one embodiment, the preferred Rayleighvalue for the each of the plurality of cells 10 is less than about300,000. More preferably, the Rayleigh value of the cell is in a rangefrom about 50,000 to about 275,000. Most preferably, the Rayleigh valueof the cell is in a range from about 125,000 to about 250,000. Based ona preferred Rayleigh value of less than about 300,000, preferreddimensions for each of the plurality of cells 10 depicted in FIG. 2 weredetermined. Preferably, the cell volume is less than about 300 cm³ withXYZ dimensions of about 7 cm by about 14 cm by about 3 cm. Morepreferably, the cell volume is less than about 145 cm³ with XYZdimensions of about 4 cm by about 12 cm by about 3 cm. Most preferably,the cell volume is less than about 100 cm³ with XYZ dimensions of about4 cm by about 8 cm by about 3 cm. In one embodiment, the cell volume maybe in a range from about 0.25 cm³ to about 2000 cm³, more specificallyin a range from about 0.25 cm³ to about 1000 cm³ and even morespecifically in a range from about 2 cm³ to about 300 cm³. Thesedimensions minimize heat transfer due to both forced and naturalconvection.

In one embodiment, the first and second sheets of material that form theplurality of cells 10 that comprise the insulative article 20 arecomprised of a fabric, such as nylon, polyester, or spandex, bonded to agas impermeable material. Examples of suitable gas impermeable materialsinclude, but are not limited to, polyethylene, polypropylene,polyurethane, urethane, silicone rubber, latex rubber,polytetrafluoroethylene (PTFE), expanded PTFE, butyl rubber, and Mylar.

FIG. 3 depicts an alternate arrangement of a plurality of cells 10 toform an insulative article 30. The cells 10 are formed as open spacebetween two layers of gas impermeable material that are joined togetherto form a plurality of cells 10. Joined regions 36 are formed betweenthe cells 10. In one embodiment, the cells 10 may be arranged in azigzag fashion with adjacent cells 10 arranged at substantially rightangles relative to one another. Each cell 10 has an X dimension 32, a Ydimension 34, and a Z dimension (not shown). The Y dimension 34 isdepicted in part by an imaginary line that extends into the adjacentcell. The cell is bounded by the dotted lines because gas atomstraveling through the center of the cell have a free motion that isessentially bounded by these dimensions since most the gas atomsbouncing off the walls will stay within this space. For purposes of thisinvention, the plurality of cells can be partially open so long as thecells are at angles that limit direct flow. In one embodiment theopening in the cell has a surface that is less than about 20% of thesurface area of the cell walls, more preferably less than about 10%, andmost preferably less than about 5 percent.

As in the previous examples, the dimensions of each of the cells 10 arechosen such that heat loss through convection is reduced or minimized.Even though the cells are connected, the formation of convectioncurrents that lead to heat loss are minimized because the right anglesbreak up the free flow path of any convection currents that may form.That is, rotational convection currents generally cannot form aroundright angles. Heat loss through convection is minimized if the Rayleighvalue for the each of the plurality of cells 10 is preferably less thanabout 300,000. More preferably, the Rayleigh value of the cell is in arange from about 50,000 to about 275,000. Most preferably, the Rayleighvalue of the cell is in a range from about 125,000 to about 250,000.Based on a preferred Rayleigh value of less than about 300,000,preferred dimensions for each of the plurality of cells 10 depicted inFIG. 3 were determined. Preferably, the cell volume is less than about300 cm³ with XYZ dimensions of about 7 cm by about 14 cm by about 3 cm.More preferably, the cell volume is less than about 145 cm³ with XYZdimensions of about 4 cm by about 12 cm by about 3 cm. Most preferably,the cell volume is less than about 100 cm³ with XYZ dimensions of about4 cm by about 8 cm by about 3 cm. These dimensions minimize heattransfer due to both forced and natural convection.

FIG. 4 depicts another alternate arrangement of a plurality of cells 10to form an insulative article 40. The arrangement is similar to thearrangement depicted in FIG. 2. The cells 10 are formed as open spacebetween two sheets of gas impermeable material that are bonded togetherto form a plurality of cells 10. Bonded regions 49 are formed betweenthe cells 10. The cells are in fluid connection with one another viaconnector tubes (46 and 48) between the cells.

As in previous examples, each of the plurality of cells 10 have an Xdimension 42, a Y dimension 44, and a Z dimension (not shown). The XYZdimensions are chosen according to the preferred Rayleigh value of lessthan 300,000 so as to minimize heat loss through convection of the gaswithin the cells 10.

FIG. 5 depicts another alternate arrangement of a plurality of cells 10to form an insulative article 50. The arrangement is similar to thearrangement depicted in FIG. 3. The cells 10 are formed as open spacebetween two sheets of gas impermeable material that are bonded togetherto form a plurality of cells 10. Bonded regions 58 are formed betweenthe cells 10. The cells are in fluid connection with one another viaconnector tubes 56 between the cells.

As in previous examples, each of the plurality of cells 10 have an Xdimension 52, a Y dimension 54, and a Z dimension (not shown). The XYZdimensions are chosen according to the preferred Rayleigh value of lessthan 300,000 so as to minimize heat loss through convection of the gaswithin the cells 10.

In one embodiment, the insulative articles depicted in FIGS. 2-10 may beused to insulate outdoor apparel. Exemplary outdoor apparel itemsinclude, but are not limited to, coats, parkas, jackets, vests, gloves,mittens, hats, liners, and boots.

In one embodiment, the insulative articles depicted in FIGS. 2-10 may beused to insulate outdoor gear. Exemplary outdoor gear items include, butare not limited to, tents, sleeping bags, bivouac bags, and sleepingpads.

III. Methods for Making an Insulative Article

A method for manufacturing a lightweight, gas-filled, highly insulativematerial can include all or apportion of the following steps: (1)providing a first sheet of a gas impermeable material and a second sheetof a gas impermeable material; (2) welding the first and seconds sheetsof gas impermeable material together to form a chamber having a cellstructure comprising a plurality cells that are in fluid communication;(3) providing a valve mechanism configured to allow an insulating gas tobe introduced into and removed from the plurality of cells; and (4)filling the plurality of cells with a dry insulating gas selected fromthe group consisting of argon, krypton, xenon, carbon dioxide, sulfurhexafluoride, and combinations thereof. In an alternative embodiment,dry atmospheric air can also be used, although the foregoing dry gasesare preferred. Preferably, the insulating gas used to fill the pluralityof cells has a moisture content less than about 4 percent by weight.More preferably, the insulating gas used to fill the plurality of cellshas a moisture content less than about 2 percent by weight. Mostpreferably, the insulating gas used to fill the plurality of cells has amoisture content less than about 1 percent by weight.

In one embodiment, the first and second sheets that form the cellularstructure comprise a fabric, such as nylon, polyester, or spandex,bonded or laminated to a gas impermeable material. Preferably thematerials used to form the insulative material are flexible such thatthe insulative material can be wearable or useable next to a person'sbody. Examples of suitable gas impermeable materials include, but arenot limited to, polyethylene, polypropylene, polyurethane, urethane,silicone rubber, latex rubber, polytetrafluoroethylene (PTFE), expandedPTFE, butyl rubber, and Mylar. In one embodiment, a portion of thebladder can also be formed of a Kevlar material and/or a laminatedKevlar material. The lamination can be any gas impermeable material orcomposition.

Exemplary techniques for joining the first and seconds sheets of gasimpermeable material together to form a chamber having a cell structurecomprising a plurality cells that are in fluid communication include,but are not limited to, ultrasonic welding, laser welding, stamp heatwelding, hot plate welding, gluing, taping, sewing, and other fabricjoining techniques known by those having skill in the art, such as, butnot limited to weaving, including one piece woven fabrics. For example,the repeating patterns of cells, examples of which are depicted in FIGS.2-10, can be formed by joining two sheets of gas impermeable fabrictogether with an ultrasonic welding drum or a hot plate welding drumthat is machined to impress the pattern into the sheets of fabric.Alternatively, the two sheets can be woven together as one piece andsealed to form chambers using techniques known in the art of makingairbags.

Exemplary techniques to welding the first and seconds sheets of gasimpermeable material together to form a chamber having a cell structurecomprising a plurality cells that are in fluid communication include,but are not limited to, ultrasonic welding, laser welding, stamp heatwelding, hot plate welding, gluing, taping, sewing, and other fabricjoining techniques known by those having skill in the art. For example,the repeating patterns of cells, examples of which are depicted in FIGS.2-10, can be formed by welding two sheets if gas impermeable fabrictogether with an ultrasonic welding drum or a hot plate welding drumthat is machined to impress the pattern into the sheets of fabric.

Heat loss through the article is lessened if convective mixing of thegas in the plurality of cells is minimized. In turn convective mixing ofthe gas in the plurality of cells is minimized if the dimensions aresuch that the Rayleigh value, which is a function of the celldimensions, is below about 300,000. In one embodiment of the presentinvention, the method further comprises choosing a volume and celldimensions for each of the plurality of cells such that the Rayleighvalue of each of the plurality of cells is less than about 300,000.Based on a preferred Rayleigh value of less than about 300,000,preferred dimensions for each of the plurality of cells 10 depicted inFIG. 3 were determined. Preferably, the cell volume is less than about300 cm³ with XYZ dimensions of about 7 cm by about 14 cm by about 3 cm.More preferably, the cell volume is less than about 145 cm³ with XYZdimensions of about 4 cm by about 12 cm by about 3 cm. Most preferably,the cell volume is less than about 100 cm³ with XYZ dimensions of about4 cm by about 8 cm by about 3 cm. These dimensions minimize heattransfer due to both forced and natural convection.

In one embodiment, the method disclosed herein further includesincorporating the insulative material into an article of outdoor appareland/or outdoor gear. Exemplary articles of outdoor apparel and/oroutdoor gear include, but are not limited to, coats, parkas, jackets,vests, pants, gloves, mittens, hats, liners, snow boots, work boots, skiboots, snowboard boots, tents, sleeping bags, bivouac bags, and sleepingpads. The insulative material can be an integral component of thearticle of outdoor gear or apparel. For example, the insulative materialcan form part of the wall of a jacket or ski pant. The insulativematerial can be used to make a hat where all or part of the hat is theinsulative material with a cellular structure. The insulative materialcan be used as a liner in a sleeping bag or it can be sewn such that theinsulative material is a permanent component of the sleeping bag. Theliner can be used as the fabric portion of the wall of a tent. Theinsulative material can be used in the floor of the tent to provide abarrier between a person and the ground. In addition, the insulativematerial can be used as a sleeping pad to provide insulated separationbetween a person and the ground.

Alternatively, the insulative material can be overlaid or attached as aliner to the article of outdoor gear or apparel. In this case, theinsulative material can be attached using a zipper, snaps, hook and loopfastener (i.e., Velcro), or any other suitable connection means. In oneembodiment, the insulative material can be incorporated into a vest orjacket that can zip into the shell of a coat. This mechanism allows theinsulative material to be selectively used or removed depending onweather condition.

FIG. 6 illustrates an insulative laminate that may include cells, suchas the cells 10 described hereinabove. The cells 10 are formed by anupper layer 62 and a lower layer 64 secured to one another at seams 66to form cells having the shapes illustrated in FIGS. 2 through 5.

In order to further reduce convection for a cell size having a givensize in the XY plane, an inner layer 68 may be positioned between theupper layer 62 and lower layer 64 in order to form cells 10 a and 10 bhaving reduced volume. In some embodiments, the inner layer 68 is gaspermeable, whereas in others it is gas impermeable. The inner layer 68may also be insulative in order to further increase the insulativeproperties of the article 60. In one embodiment, the inner layer 168 isa closed cell foam or an open celled foam. Open celled foam can be usedwhere the insulative article is to be compressed (e.g., for storage).The open celled foam allows the insulative gas to flow out of the foamcells when the bladder is being deflated and the article compressed. Ina preferred embodiment, the inner layer 66 is formed of an insulativesynthetic fiber such as THINSULATE™, PRIMALOFT™, or the like. The innerlayer 68 inhibits convection within the cells thereby reducing heattransfer. As with other embodiments described herein, an insulative gas,such as argon may be injected into or released from the cells 10.

The inner layer 68 may be secured to the upper layer 62 and 64 by theseams 66. The seams 66 may be formed according to the methods describedhereinabove. In some embodiments, where the seams 66 are formed byultrasonic, or other, welding techniques, the upper layer 62 and lowerlayer 64 may permeate the inner layer 68 in order to secure to oneanother and the inner layer 68.

In another embodiment of an insulative laminate material 70 isillustrated in FIGS. 7 through 10. In the embodiments of FIGS. 7 through10, the cells 10 are formed by an upper gas impermeable layer 71 and alower gas impermeable layer 73 that form the air chamber. A plurality ofinterior or middle layers 74 divide the space between impermeable layers71 and 73 to form an upper layer of cells 10 a and a lower layer ofcells 10 b. Interior layers 74 are attached to upper layer 71 at wall76, which forms a seam between cells 10 a of upper layer 71. Interiorlayers 74 are also attached at walls 80, which form a seam between cells10 b. While the seams 76 and 80 are shown as spanning a relatively largearea of a cell, those skilled in the art will recognize that the walls76 and 80 can have any length depending on the technique used to jointhe interior layers. In one embodiment, the seams can be as narrow asthe thickness of the material of interior layers 74. Interior layers 74may or may not be gas impermeable since these layers are within the airchamber formed by joining gas impermeable layers 71 and 73.

In FIG. 8, the walls 80 (i.e., the seams of the layer of cells 10 b) areat least partially offset from the walls 76 (i.e., the seam of the layerof cells 10 a). The article 70 of FIGS. 7 and 8 may be formed using anytechnique including lamination, weaving, welding, adhesives, stitching,and the like.

In one embodiment, article 70 may be manufactured using a spacer and afabric welding technique. In this embodiment, middle layer 74 is firstsecured to upper layer 71. Next a spacer is positioned in the upperlayer of cells 10 a and lower layer 73 is welding to the layer of cells10 a at a location other than the seam, so as to create an overlap withthe cells and the seams. The spacer can then be removed from cells 10 a.The use of the spacer prevents wall 80 from being welded to wall 72,thereby preserving the first layer of cells during formation of thesecond layer of cells. This embodiment is advantageous for forminggas-impermeable interior layers 74.

In an alternative embodiment, layers 71, 73 and interior layers 74 canbe joined together and then laminated to make layers 71 and 73 gasimpermeable. For example, layers 71, 73 and 74 can be woven and thenlaminated using lamination techniques known in the art. In oneembodiment, layers 71 and 73 may be made gas impermeable by laminatingwith a material selected from the group including polyethylene,polypropylene, polyurethane, urethane, silicone rubber, latex rubber,polytetrafluoroethylene (PTFE), expanded PTFE, butyl rubber, and/orMylar and/or materials that provide a similar functionality.

Yet another alternative embodiment is described with reference to FIG. 9in which an interior layer 74 a is a single continuous layer. In FIG. 9,the layered laminate material 70 may be formed by coupling an upperlayer 71 a to an intermediate or interior layer 74 a to form seams 76 a.The lower layer 73 a may then be coupled to the intermediate layer 74 aby means of an adhesive or other fastening means. The seams 76 a arepreferably offset from the seams 80 a as in the embodiment describedwith respect to FIG. 8. As with other embodiments described herein, aninsulative gas, such as argon may be injected into or released from thecells 10 a and/or 10 b. The present invention includes insulativematerials with any number of layers having cells and or subcells formedtherein. In addition, all or some of the layers may be offset orpatterned so as to position the insulative portion of the cells of onelayer above the seams of another layer.

The configuration of the cells in FIGS. 8 and 9 can be achieved for thearrangement of cells illustrated in FIGS. 2 through 5 and/or any otherarrangement of cells where the cells can be layered. Moreover, the cellsdo not need to have a rectangular shape. In some embodiments, the cellscan polygonal and/or spheroidal. FIG. 10 illustrates a portion of aninsulative material 150 that includes spheroidal shaped cells. An upperlayer of cells 152 is disposed above a lower layer of cells 154. Thespheroidal cells 152 are offset from spheroidal cells 154 such that theseams of the cells in the layers are insulated by the adjacent layer 152or 154. In one embodiment, spheroidal cells 152 and 154 have a crosssection similar to FIG. 8.

The cells of the insulative layer can also vary in size in certainregions of the insulative material. The various sizes can be selected tomaximize insulation where insulation is most needed and minimize thevolume of gas for other locations where insulation is not as important.In one embodiment, the insulative material can include regionsconfigured to provide increased insulation (relative to other regions ofthe insulative material) for certain body parts of a person.

For example, the insulative material can be configured to provideincreased insulation to regions of the body, including, but not limitedto a head region, a shoulder region, a hip region, or a calf region of aperson's body or a subportion of any of these regions.

The increased insulation can be provided by increasing the thickness ofthe insulative material. In one embodiment, the thickness can be in arange from about 0.5 cm to about 20 cm, more preferably about 1 cm toabout 10 cm, and most preferably about 1.5 cm to about 5 cm. In oneembodiment, the difference in the thickness between the differentlysized cells in different regions of the insulative material is in arange from about 1.1 to about 20 times the thickness, more specificallyabout 1.2 to about 10 times the thickness, and even more specificallyabout 1.3 to about 5 times the thickness.

FIG. 11 illustrates an example of an article of outdoor gear or apparelincorporating cells with different thicknesses in different regions ofthe insulative material. FIG. 11 illustrates a sleeping pad 110 having asurface sized and configured to support a person lying thereon. Forexample, the sleeping pad 110 may include a cell structure suitable forwithstanding pressures needed to support a person weighing between 20 kgto 120 kg. The sleeping pad 110 may have a width in a range from 40 cmto 100 cm, more specifically 60 cm to 80 centimeters, a length in arange from 140 cm to about 250 cm, more specifically 170 to 200centimeters, and a height (i.e., thickness) in a range from 1 cm toabout 20 cm, more specifically 3 cm to 10 centimeters

Sleeping pad 110 has a head portion 112, a torso portion 114 and a lowerextremity portion 116. Each portion, 112, 114, and 116 may includeregions configured to provide increased or decreased insulationdepending on the relative importance of the region. For example, in oneembodiment, increased insulation can be provided by head region 118,shoulder region 120, hip region 122, and calf region 124. Regions 118,120 and 124 are positioned and configured to engage the head, shoulders,hips, and calf, respectively of a person lying on sleeping pad 110.Moreover, sleeping pad 110 includes lesser insulated regions 126, 128,130, and 132. In a preferred embodiment, the lesser insulated regionscover a larger percentage of the sleeping pad at the periphery, whilethe more highly insulated regions cover a larger percentage of thesleeping pad near the center.

The insulative material of sleeping pad 110 includes first and secondgas impermeable layers joined together to form a chamber having a cellstructure including a plurality cells that are in fluid communication.One or more interior layers of material are positioned within thechamber between the first and second gas impermeable layers. the one ormore interior layers divide the chamber into the plurality of cells. Theplurality of cells may form a first layer of cells above a second layerof cells. Any of the cellular structures described above with respect toFIGS. 1-10 or a similar structure can be incorporated into sleeping pad110.

The increased insulation may be provided by incorporating thicker cellsinto regions 118, 120, 122, and 124, as compared to regions 126, 128,130, and 132, respectively. The thicker regions may be thicker by about1.1 to about 4 times, more specifically about 1.2 to about 3 times, andeven more specifically about 1.3 to about 2 times. In one embodiment,these ranges allow thicker regions of insulation without abrupt changesin the contour. The use of thicker and thinner regions is advantageousbecause the overall volume of the sleeping pad can be reduced and/or theeffective insulative potential increased compared to a sleeping pad thatmaintains the same cell size throughout.

Sleeping pad 110 also includes a valve mechanism 134 that allows a gasto be introduced into sleeping pad 110. Any of the gasses and/or valvemechanisms described herein can be used in conjunction with theinsulative material incorporated into sleeping pad 110. The valvemechanism 134 can be actuated by blowing (e.g., by mouth) and/or byusing a fillings system as described below with reference to FIG. 14.Alternatively, valve mechanism 134 can be actuated using a hand or footpump and/or using an electric pump to inflate the cells.

The insulative materials with two or more layers of cells as describedwith respect to FIGS. 7-10 can be incorporated into any outdoor gear orapparel where flexible insulation is desirable. Examples of outdoor gearthat can utilize the layered insulative materials described hereininclude a tent, a sleeping bag, a bivouac bag, or a sleeping pad, or thelike. Examples of outdoor apparel that can incorporate the layeredinsulative material includes, but is not limited, a vest, jacket, glove,pant, boot, or the like.

FIG. 12 illustrates a wearable item 90 that includes an insulationmaterial having cells 10 formed according to any of the layeredmaterials described above with respect to FIGS. 2-10. The cells 10 maybe in fluid communication with an inlet valve 92. The inlet valve 92 maybe secured to an outer surface of the wearable item. The inlet valve 92may be secured to the wearable item 90 by means of adhesive, welding, orthe like.

Referring to FIG. 13, in another embodiment, an insulative pad 82 isformed of an upper layer 84 and a lower layer 86 joined at theirperimeters to define a cavity. A foam layer 88 may be positioned betweenthe upper layer 84 and lower layer 86. The foam layer 88 is preferablyformed of an open-cell foam. The foam layer 88 preferably occupiessubstantially the entire volume defined by the upper layer 84 and lowerlayer 86, such as between 80 and 95 percent of the volume. The pad 82may be sized to support a sleeping person. For example, the upper layer84 and lower layer 86 may define a volume have a width of between 60 and80 centimeters, a length of between 170 and 200 centimeters, and aheight of between 3 and 10 centimeters. As with other embodimentsdescribed herein, an insulative gas such as argon may be injected intoor released from the pad 82 by means of a valve or some other meanspermitting the inflation and deflation of the pad 82.

IV. System for Inflation of Insulative Material

The present invention includes a system for inflating and deflating agas bladder of an insulative material as described above. For examplethe inflation system can be used to deliver a gas, (e.g., a dry gas) tosleeping pad 110 through valve 134 or into jacket 90 using valve 92.Referring to FIG. 14, an inflation device 94, may be selectively coupledto valves 134 or 92. The filling apparatus 94 may include a gasreservoir 96, a housing 98, an outlet valve 100, an outlet orifice 102,and a shroud 104. The gas reservoir 96 is secured to the housing 98,such as by means of threads formed on the reservoir 96 engagingcorresponding threads on the housing 98. In some embodiments, a spike 99may be positioned to pierce a membrane of the gas reservoir as thereservoir 96 is threaded into the housing 98. The gas reservoir 96 is influid communication with the valve 100 such that the valve 100 controlsthe release of gas from the reservoir 96 when it is coupled to thehousing 98.

The valve 100 is preferably manually actuated, such as by means ofpressing a button or lever. The valve 100 is in fluid communication withthe outlet orifice 102 such that gas is released through the orifice 102when the valve 100 is manually actuated. In some embodiments, a pressureregulator 105 may be positioned in the fluid path between the gasreservoir 96 and the orifice 102 to reduce the output pressure. Theshroud 104 surrounds the orifice 102 and performs at least one of twofunctions: coupling the portable filling apparatus 94 to the valve 92 or134 of the wearable item 90 or sleeping pad 110 and providing a sealbetween the valve 92 or 134 and itself In some embodiments, a post 106projects outwardly adjacent the orifice in order to depress the valve 92or 134 when the portable filling apparatus 94 is engaged with the valve92 or 134.

The portable filling apparatus 94 may include means for hinderingdecoupling of the portable filling apparatus 94 from the valve 92. Themeans for hindering decoupling may also function as means for creating aseal between the portable filling apparatus 94 and the valve 92 or 134.

For example, the portable filling apparatus 94 may include a frictionfit mechanism, a snap-connect mechanism, or a magnet coupler.

A gas such as air or an inert gas is disposed in portable fillingapparatus 94. Where an inert gas is used, the inert gas may be one ormore of argon, krypton, or nitrogen. For purposes of this invention, theterm nitrogen shall mean diatomic nitrogen, unless otherwise specified.The inert gas is compressed in the canister at a pressure of at least1000 psi, more preferably at least about 2500, even more preferably atleast about 3000 psi, and most preferably at least about 3500 psi orhigher. Pressures of at least 2200 psi are important for some embodimentwhere a relatively large bladder is used. In an alternative embodiment,the pressure volume is at least about 200 MPa-cm³, more specifically 400200 MPa-cm³, and 600 MPa-cm³. For example to fill an adult size jacketwith argon, a pressure of 2200 provides sufficient pressure to ensurethat the jacket can be fully inflated. The higher pressures listed aboveare preferred because they allow additional fills of a jacket or otherarticle without reconnecting a new canister. Using higher pressures isimportant to some applications in order to obtain a canister that isreasonably portable, light weight, cost effective, and providessufficient gas for inflating an article of outdoor gear and apparel.

For the gas canister to be useful in some cold weather applications, thecanister may include a gas that undergoes little or no liquefaction atambient temperatures and pressures in a range from 2000-6000 psi. If thegas in the canister is a liquid (e.g., carbon dioxide), rapid expansionof the gas causes cooling, which can cause a gas filling apparatus tomalfunction in cold weather. Examples of suitable insulative gases thatcan be compressed to high pressures without substantial liquefactioninclude argon, krypton, and nitrogen. Argon and krypton are particularlypreferred for their insulative properties in addition to theirsuitability for being compressed in a gas canister and rapidly expandedthrough a gas filling apparatus.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A layered insulative material incorporated into an article of outdoorgear or apparel, comprising: first and second gas impermeable layersjoined together to form a chamber having a cell structure comprising aplurality cells that are in fluid communication; and one or moreinterior layers of material positioned within the chamber between thefirst and second gas impermeable layers, the one or more interior layersdividing the chamber into the plurality of cells, wherein the pluralityof cells form a first layer of cells above a second layer of cells; anda valve mechanism coupled to the insulative material and configured toallow inflation and deflation of the plurality of cells of the first andsecond layers of cells.
 2. An insulative material as in claim 1, whereinthe cell volume is in a range from about 0.25 cm³ to about 2000 cm³. 3.An insulative material as in claim 1, wherein the cell volume is in arange from about 0.25 cm³ to about 1000 cm³.
 4. An insulative materialas in claim 1, wherein the cell volume is in a range from about 2 cm³ toabout 300 cm³.
 5. An insulative material as in claim 1, wherein thefirst and second gas impermeable layers include a woven material.
 6. Aninsulative material as in claim 5, wherein each of the gas impermeablelayers includes a gas impermeable laminate material.
 7. An insulativematerial as in claim 6, wherein the gas impermeable laminate material isselected from the group consisting of polyethylene, polypropylene,polyurethane, urethane, silicone rubber, latex rubber,polytetrafluoroethylene (PTFE), expanded PTFE, butyl rubber, and Mylar.8. An insulative material as in claim 1 further comprising welding aportion of the first and seconds gas impermeable layers together to formthe chamber.
 9. An insulative material as in claim 8, wherein thewelding forms seams that at least partially defines the cells of theplurality of cells.
 10. An article of outdoor gear or apparel includingan insulative material as in claim 1, the article further comprising adry gas reservoir configured to allow a dry insulating gas to beintroduced into the plurality of cells.
 11. An article of outdoor gearor apparel as in claim 10, wherein the dimensions of the plurality ofcells are such that the Rayleigh value of the dry insulating gas withinthe plurality of cells is less than 300,000 for each cell.
 12. Anarticle of outdoor gear or apparel as in claim 10, wherein the dryinsulating gas is dry atmospheric air having a moisture content lessthan about 4 percent by weight.
 13. An article of outdoor gear orapparel as in claim 10, wherein the dry insulating gas is selected fromthe group consisting of argon, krypton, xenon, carbon dioxide, sulfurhexafluoride, and combinations thereof.
 14. An article of outdoor gearor apparel as in claim 10, wherein the insulative material isincorporated into a coat, a parka, a jacket, a vest, a pant, a glove, amitten, a hat, a liner, a wader, a boot, a tent, a sleeping bag, abivouac bag, or a sleeping pad.
 15. A method for using an article ofoutdoor gear or apparel, comprising: providing an article of outdoorgear or apparel according to the method of claim 10; and filling theplurality of cells with a dry insulating gas selected from the groupconsisting of atmospheric air, argon, krypton, xenon, carbon dioxide,sulfur hexafluoride, and combinations thereof, wherein the insulatinggas has a moisture content less than about 4 percent by weight.
 16. Alayered insulative material incorporated into an article of outdoor gearor apparel, comprising: an insulative material including first andsecond gas impermeable layers joined together to form a chamber having acell structure comprising a plurality cells that are in fluidcommunication; and one or more interior layers of material positionedwithin the chamber between the first and second gas impermeable layers,the one or more interior layers dividing the chamber into the pluralityof cells, wherein the plurality of cells form a first layer of cellsabove a second layer of cells, the first layer of cells including seamsbetween the cells of the first layer; the second layer of cellsincluding seams between the cells of the second layer; wherein at leasta portion of the cells of the first layer of cells overlap with aportion of the seams of the second layer of cells; and wherein at leasta portion of the cells of the second layer of cells overlap with aportion of the seams of the first layer of cells; and a valve mechanismcoupled to the insulative material and configured to allow inflation anddeflation of the plurality of cells of the first and second layers ofcells.
 17. An insulative material as in claim 16, wherein the first andsecond gas impermeable layers are woven.
 18. A sleeping padincorporating a layered insulative material, comprising: a sleepingsurface sized and configured to support a person lying thereon; and alayered insulative material comprising, first and second gas impermeablelayers joined together to form a chamber having a cell structurecomprising a plurality cells that are in fluid communication; and one ormore interior layers of material positioned within the chamber betweenthe first and second gas impermeable layers, the one or more interiorlayers dividing the chamber into the plurality of cells, wherein theplurality of cells form a first layer of cells above a second layer ofcells; and a valve mechanism coupled to the insulative material andconfigured to allow inflation and deflation of the plurality of cells ofthe first and second layers of cells.
 19. A sleeping pad as in claim 18,wherein, the first layer of cells includes seams between the cells ofthe first layer; the second layer of cells includes seams between thecells of the second layer; at least a portion of the cells of the firstlayer of cells overlap with a portion of the seams of the second layerof cells; and at least a portion of the cells of the second layer ofcells overlap with a portion of the seams of the first layer of cells.20. A sleeping pad as in claim 19, wherein the first and second gasimpermeable layers are woven.
 21. A sleeping pad as in claim 18, whereincertain regions of the camping pad have different sized cells comparedto other regions of the camping pad.
 22. A sleeping pad as in claim 21,wherein the average thickness of the cells in a region of the sleepingpad configured to support the torso portion of a person is thicker thana region of the sleeping pad configured to support the legs of a person.